(i) Field to which invention relates
The present invention relates to a cleaning machine for castings having a cleaning drum with a blast opening stretching in the length-direction thereof, a system for driving the cleaning drum oscillatingly about its long-axis with a center angle of about 120.degree., and with one or more abrasive throwing wheels placed over a blast opening, said drum being placed sloping from an inlet opening at one end thereof downwards to an opposite outlet opening.
(ii) The prior art
Unlike batch-operation cleaning machines, cleaning drums of the sort noted are responsible for the useful effect of continuous operation, the castings being run into the drum at one end and, on motion through the drum, at an adjustable speed if necessary, are blasted and are then continuously taken from the other end of the drum. To make it unnecessary for the abrasive throwing wheels to be moved with their supply pipes for the blasting abrasive, such wheels are stationarily positioned. The cleaning drum is moved, together with its peripheral blast opening, backwards and forwards under the abrasive throwing wheels. The center angle of this oscillating motion, and, for this reason, the breadth of the blast opening are generally dependent on the desired degree of filling of the drum and on the need for turning over the castings in the drum as completely as possible. In this respect a center angle of about 120.degree. of oscillation has turned out to be of good effect. However, the need for complete turning over or tumbling of the castings is very much harder to take care of in the case of oscillating cleaning drums than in the case of batch operation drums, which are continuously kept turning.
In one earlier design (see the German Offenlegungsschrift specification No. 2,424,086) the cleaning drum has a part-cylindrical cross-section. At the edges of its opening, the drum wall is bent inwards at an angle for making possible the greatest possible center angle of oscillating motion without there being any danger of the castings' falling out past the edge of said opening. However, the number of different forms of castings which may be cleaned with the desired effect in such a drum is limited, because of slipping of the castings in the drum against the cylindrical drum walling without the desired tumbling or rolling over effect being produced. For this reason, for general works use, drums of this design have to have complex inner structures, in order to make certain that the castings are in fact turned and blasted on all sides. It is furthermore necessary for the drum's inner structures to have to be designed in line with the forms of the castings in question to make certain, on the one hand, of complete rolling or tumbling of the castings, while, on the other hand, not damaging less strong sorts of castings. All this makes a great number of tests necessary before a production run may be undertaken with the cleaning machine.
In addition to such prior art cleaning machines having a rigid cleaning drum, designs have been put forward in which the drum wall is in the form of an oscillating troughed transport belt or a continuously turning armored chain (see British Pat. No. 801,683 and Swiss Pat. No. 68,860). However, with respect to the turning over of the castings there are the same shortcomings in this respect as with cleaning drums having a stiff wall. In addition, there are shortcomings with respect to function, because such belts have to be made of wear-resistant material, that is to say belts with scales as armor. Furthermore, such designs are generally very high in price.